Hi All,
I just found out some information that I was unaware of. To prevent air from getting trapped in the housing of your march pump, you need to have the discharge pointed up. I have mine pointing down. According to the tech guys in engineering at March Pumps, there will always be air trapped in the top of your housing when the discharge is pointing down. The purge valves we are using will not help this problem.

So, I need to replumb my pumps so that the suction is on the bottom and the discharge is on the top.

One intriguing solution is to drill a hole at the highest point of the housing, tap it and install the purge valve there. I don't have the tap and die set or the expertise to do this, or that would be the solution I would go with instead of a major re-plumb of the pumps.

I spent all afternoon swapping my lines around, which meant cutting and bending a lot of tubing. But, I finally got it finished. It's not pretty, but I'll be sure and let everyone know if it fixes my problems with priming.

It's little gems like this that need to be caveats. ie. always discharge your pump to the top...would have saved me a lot of work.

Last edited by Mob_Barley on Tue Feb 01, 2011 9:44 am, edited 1 time in total.

I have my pump manifold hooked up this way, but I still haven't had the opportunity to try it out. It seems logical to me though. You're using gravity to help push the air out of your pump and fill it with water/wort from the bottom, up. There's really nowhere for air to get trapped inside your pump housing when you do it this way.
I'd definitely like to know if it fixes your priming issues. I have a bleedoff valve hooked up to the discharge part of my manifold. I wasn't planning on using the purge valves that I see on everyone else's rig. At least at first.

It's a little off topic, I know, but is there any other reason for using the purge valves besides initially priming your pumps?

In extreme circumstances, the assailants can be stopped by removing the head or destroying the brain. I will repeat that: by removing the head or destroying the brain. - News Anchor, Shaun of the Dead

It took me a little while to visualize the problem. The way I see it you will always get a little air in your lines at some point. The air bubbles are going to try and rise to the top, so they will sit at the top of the pump housing, above the impeller. If you have your suction on the top, you will always be pushing fluid down into the pump and the air cannot rise or flow out of the top of the housing against this flow. But when you have your pump discharge on top, the air gets circulated out with the discharging fluid and thus won't be sitting trapped in the top of your pump housing. The pump gets primed more quickly this way...in theory.

I'll have to try it out when I get back from this job, or at the end of the month when I come in for Mardi Gras...unless someone else tries it and posts their results first.

I have doubts as to whether air can remain trapped in the housing once fluid is flowing, but I don't see any harm in doing it as you say. Though after looking at the housing on my March pumps, I suspect a horizontal configuration would do just as well as long as the outflow is on top. That means easier brewing for people who brew left-to right rather than right-to left. At least with the configuration of my pumps.
Unfortunately for me, the information I got when I bought my pumps said that they would work in any direction, so I designed my RIMS right-to-left. However, Redtail's pumps are mounted in a vertical orientation and he experiences no cavitation even at a full boil, so I have admit you are right on this one.

I'm not sure whether the orientation of the pump head will affect cavitation or not. Cavitation is a complicated phenomenon which occurs in fluid dynamics. It all has to do with the fact that the pump is getting starved for fluid on the suction side (at least that's my understanding for the cause in a RIMS setup). This fluid starvation is due to restrictions in flow on the suction side, either the lines are too small to feed the full amount of fluid that the pump needs, or there are other restrictions in the line which are starving the pump of fluid.

The orientation of the head is supposed to fix the problem of priming, which is an altogether different problem. But, maybe it can fix both, I'm not a fluids engineer.

I'm not a fluids engineer either, so maybe I used the wrong term. All I know for sure is that you appear to be right about the pump head orientation. Also i have found that restricting the input side of the March pumps does not appear to cause any problems with pumping. It makes intuitive sense to me that if the outflow is restricted as much or more than the input, then the pressure should equalize enough that it will not affect the pump's performance other than to reduce the total flow rate. This appears to be the case from what I've seen in operation.
Regardless, I think you're 100% correct regarding the pump head orientation. I guess I need to reconfigure my pumps too.